From: Michal Hocko <mhocko@kernel.org>
To: "Shi, Yang" <yang.shi@linaro.org>
Cc: tj@kernel.org, jack@suse.cz, axboe@fb.com,
fengguang.wu@intel.com, akpm@linux-foundation.org,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
linaro-kernel@lists.linaro.org
Subject: Re: [RFC PATCH] writeback: move list_lock down into the for loop
Date: Mon, 29 Feb 2016 18:33:12 +0100 [thread overview]
Message-ID: <20160229173312.GK16930@dhcp22.suse.cz> (raw)
In-Reply-To: <56D47F90.9050903@linaro.org>
On Mon 29-02-16 09:27:44, Shi, Yang wrote:
> On 2/29/2016 7:06 AM, Michal Hocko wrote:
> >On Fri 26-02-16 08:46:25, Yang Shi wrote:
> >>The list_lock was moved outside the for loop by commit
> >>e8dfc30582995ae12454cda517b17d6294175b07 ("writeback: elevate queue_io()
> >>into wb_writeback())", however, the commit log says "No behavior change", so
> >>it sounds safe to have the list_lock acquired inside the for loop as it did
> >>before.
> >>Leave tracepoints outside the critical area since tracepoints already have
> >>preempt disabled.
> >
> >The patch says what but it completely misses the why part.
>
> I'm just wondering the finer grained lock may reach a little better
> performance, i.e. more likely for preempt, lower latency.
If this is supposed to be a performance enhancement then some numbers
would definitely make it easier to get in. Or even an arguments to back
your theory. Basing your argument on 4+ years commit doesn't really seem
sound... Just to make it clear, I am not opposing the patch I just
stumbled over it and the changelog was just too terrible which made me
response.
--
Michal Hocko
SUSE Labs
prev parent reply other threads:[~2016-02-29 17:33 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-26 16:46 [RFC PATCH] writeback: move list_lock down into the for loop Yang Shi
2016-02-29 15:06 ` Michal Hocko
2016-02-29 17:27 ` Shi, Yang
2016-02-29 17:33 ` Michal Hocko [this message]
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